When recalling memories, neural activity is sparked in different brain regions
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Even forgotten memories appear to influence our behavior.
“People often perceive memories as something to reflect on or contemplate,” says Nick Turk Brown from Yale University, who was not involved in this research. “However, we don’t spend our days lost in past memories. We work, parent, and have fun. Our memories continuously shape our actions; I believe 95% of our cognitive processes operate in this unseen manner.”
Memory can be described in various ways. One perspective focuses on self-reported recollections, like what someone had for dinner yesterday or details about their seventh birthday. Another way to conceptualize memory involves the persistent networks of brain cells known as engrams, which create the biological representation of experiences we have memorized.
Many researchers have long believed that forgetting a memory implies the disappearance of its related engrams. However, studies on mice suggest that forgotten memories endure even when they cannot be consciously retrieved.
In a study led by Tom Willems from the University of Bern, Switzerland, 40 participants briefly viewed 96 pairs of images, including human faces and objects like guitars and staplers.
The researchers then monitored the participants’ brain activity while testing their memory of whether two images had been paired 24 hours prior, using high-resolution functional magnetic resonance imaging. Participants were also asked if they remembered seeing the images together, if they were uncertain, or if they were just guessing.
When they confidently recalled the images, participants correctly chose the paired images 87% of the time in both tests. Conversely, those who could not recall what they had seen managed to achieve about a 50% accuracy rate.
Participants uncertain of their memory estimated correctly 57% of the time after both 30 minutes and 24 hours, suggesting that this group may still retain some memory of the associations.
Interestingly, when guessers made the right choice, their brain activity patterns mirrored those of participants who confidently remembered, particularly in the relevant hippocampal regions.
During a follow-up test after 24 hours, individuals who believed they had forgotten remained active in the hippocampus, while those who recognized the images exhibited activity in the anterior cingulate gyrus of the neocortex.
As Amy Milton from Cambridge University states, “I suggest that the shift of memory activity to the neocortex is associated with recall, but it remains unclear whether this change is a cause or a result of what is remembered.”
Nevertheless, the findings align with a predominant theory of memory function, known as Standard Integration Theory, as explained by Turk Brown. This theory proposes that memories are initially formed in the hippocampus and later consolidated in the neocortex during sleep for long-term storage.
This research highlights a potential separation between the memories we consciously access and the associated engrams in the brain, according to Turk-Browne. “This offers a fascinating illustration of the subtle, automatic, and pervasive influence of hippocampal memories on behavior.”
“Essentially, what they propose is that some memories don’t have to be consciously searched for in order to influence behavior later,” Milton explains.
She expresses no surprise that strong memory traces can shape our actions without our conscious awareness, referencing the phenomenon of priming. Seeing or hearing something can subtly prompt specific responses without us discerning the reasons.
However, priming occurs in various brain regions, such as the prefrontal cortex, and as Turk-Browne notes, it typically produces only transient effects lasting seconds or minutes.
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Source: www.newscientist.com
